Take time=7ms (approx. dead time of a rectified mains sinewave), current=half the primary current (it's only drawn from each capacitor bank during half of the time, so average value is halved), and capacitance=the value for a single bank.

First off, mzzj: I don't t hink I swapped my #s, but I may have worded my question to Alex a little poorly. Nothing gets past this crowd! I referred to F(osc) and F(sw) because, as we all know, for dual-channel PWM chips, F(osc) =2F(sw). That's where the confusion may have come in.

Alex,

My primary was 38T of #22 (tri-filar), V(pri) was 160V (Voltage doubler for 120VAC on our side of the Pond). The primary turns equation I used came from Chryssis' book, chapter 4 "The High Frequency Power Transformer". I will have to dig out the equation, but after a fashion, I had reduced the transformer design process down to 8-12 very concrete cut-n-dried steps. The variation in the number of steps was determined by the complexity of the transformer (# of secondaries, etc.). When i find the equation, I will also type out my design process. For the timing and compensation components:
R(t) = 2.21KW
C(t) = 10nF
R(d) = 0W,

yielding an oscillator frequency of = 64.6kHz, and a switching frequency of 32.32kHz.

Compensation at pin 9 is 49.9kW paralleled with 1000pF, going to ground. Opto current was set a 1mA over 60V (so 60kW. No Zener, but in a previous version, I did use a TL431 for a reference, compensated at the TL431. Have to go for now (child is stirring from nap), but I will be back soon.

How do you derive the 12V for the PWM & Driver chips? I gather it is an auxiliary winding on the main core. Do you use a Zener-pass regulator for the start-up ckt?

This is how I did mine. TIP50 (400Vce) with a 16kW power resistor in series from the high-voltage bus (~320-330VDC) to the collector of the TIP. 1N5242 (12V 500mW) and 440kW provide the reference for the transistor. My auxiliary winding put out ~16V, so when it started producing voltage, this automatically shut down the start-up ckt. The SG3525 needs a start-up ckt capable of providing atleast 50mA, beacuse it's start-up current is the same as it's operating current, ~20mA. As mzzj stated, 200mA should be enough to power the '3525 and the '2113.

I have decided to rebuild this power supply, as I still have most of the parts lying around. I think I will replace the IRF740s (400Vdss) with IRF840s (500Vdss), because I might want to PFC the front end. Everything else, except the transformer's primary turns, I think I will keep the same.

Oh yeah, one other thing- I found that stacking two toroid cores helped me in the power capacity department. I've done this using the same FT-140-77 cores for some 12V push-pull converters I did in the past. Haven't tried it for off-line yet. This might be worth looking into. Sure, it will change some of your numbers around, but you will have more headroom and avoid core saturation.

If it's because of what I suspect, probably his '2113 caused one or both of the '740s to blow. Perhaps the floating drive for the upper MOSFET crapped out. This happened to me. After I took apart my 3525-2113 based PSU, I tried to re-do it on a pc board. Powered it up, and the 2113 and one of the IRFP350s (TO-247 version of the '740) promptly let the Magic Smoke out. This led to the failure of the lower MOSFET about a second and a half later. I did not have a can of magic smoke to put back in.....

I believe in one of the other threads, eva, you stated your reluctance to use these floating gate-driver ICs because they tend to fail more often than not. I bleieve you said that driver transformers were still better from a reliability standpoint. Please correct me if I'm wrong.

I have a few IR2112 in an antistatic bag somewhere, they look fancy but I have never used them. I feel more attracted towards transformers as they allow to provide both power and signal to your own custom gate drive circuit, that may be as simple as a PNP transistor to speed up turn-off and a couple of resistors and diodes, while keeping galvanic isolation and allowing for secondary-side control. Also, transformers doesn't blow everytime a power device dies, and they protect the control circuit.